Method for flameproofing combustible materials

ABSTRACT

A PROCESS FOR FLAMESPROOFING COMBUSTIBLE MATERIALS BY ELECTRODEPOSITING VERMICULITE FROM AN AQUEOUS SOLUTION OF AN ALKALI METAL SALT ONTO SAID MATERIALS.

3,567,613 METHOD FOR FLAMEPROOFING COMBUSTIBLE MATERIALS John W. Kraus, Fairfax, Va., and Jose E. Herrera, Ellicott City, Md., assignors to W. R. Grace 8; Co., New York, N.Y. No Drawing. Filed May 10, 1968, Ser. No. 728,357 Int. Cl. B01k 5/02 US. Cl. 204181 8 Claims ABSTRACT OF THE DISCLOSURE A process for flameproofing combustible materials by electrodepositing vermiculite from an aqueous solution of an alkali metal salt onto said materials.

The term vermiculite, used herein, refers to the group of rock forming mineral species characterized by a layer lattice structure in which the silicate layer units have a thickness of approximately 10 Angstroms. The main elements present in the layer are magnesium, aluminum, silicon, and oxygen with the layers being separated by one or two sheets of water molecules associated with cations such as magnesium, calcium, sodium, and hydrogen. The layers have considerable lateral extent relative to the thickness of the basic 10 Angstrom unit layer. The term vermiculite, as used herein, therefore, includes minerals consisting wholly or largely of vermiculite or minerals of mixed layer type containing vermiculite layers as important constituents such as hydrobiotites, chlorite vermiculites, but does not include minerals of the montmorillonite group. Very broadly, the present invention relates to a method of rendering paper, fabrics, and other combustible materials flame resistant by electrodeposition of a layer of vermiculite on the surface of the combustible materials.

The phenomena described in this application are directly attributable to the fact that the layer-silicate platelets dispersed in a liquid medium carry a net electrical charge. This electrical charge arises by virtue of the fact that the layer silicates possess numerous sites relatively high in electron density, as a result of isomorphous substitution of cations within the tetrahedral and octahedral layers of the crystal lattice. Chemical ion exchange causes replacement of the exchangeable cations bound to the tetrahedral layers of the silicate mineral producing platelets that behave in a manner characteristic of a given cation. Thus, protonated vermiculite (H /Vm) behaves somewhat different from a sodium vermiculite (Na+/Vm).

If the charged platelets are dispersed in a liquid medium and an electrical potential is applied between two conductors or metal electrodes, the charged platelets will migrate through the medium towards a particular electrode, where the direction of migration is dependent on the sign of the net charge, whether negative or positive. If the net charge on the platelet face is negative, the platelets will move towards the anode, whereas a net positive charge will cause the platelets to move toward the cathode.

Normally, the natural mineral-layer silicates possess a net negative charge on the platelet faces, and the charge magnitude varies from mineral to mineral.

The migrating charged particles ultimately contact the appropriate electrode where they are discharged, by gain or loss of an electron. It has been demonstrated that paper, cloth, and other combustible materials can be coated by proper electrode configuration so as to render the material waterproof and reduce its flammability. This is accomplished by mounting the material to be coated between two electrode compartments; in one compartment is placed a dispersion of the layer silicate while the second com- Jnited States Patent Gfice 3,567,613 Patented Mar. 2, 1971 partment contains an organic salt. As a potential is impressed across the electrodes of the cell, the negatively charged silicate particles migrate toward the anode but are deposited on the barrier of combustible materials. Simultaneously, the organic salt (generally an amine salt or urea) moves towards the cathode and on contacting the charged particles discharge them and render the deposit fast on the matrix of the barrier.

The slurry used to furnish the vermiculite for the electrodeposition is prepared as follows: The vermiculite is soaked in an aqueous salt (NaCl) solution and then washed with water. Following this, the vermiculite is steeped for an extended period of time in a concentrated aqueous solution of a lithium salt. The treated vermiculite is then washed with water and allowed to stand in water with consequent swelling of the vermiculite ore. The swelling or expansion of the vermiculite is many fold and takes place along the axis perpendicular to the basal plain of the mineral crystal. This is due to the treatment of the ore previously described in which ion exchange takes place between the preferred monovalent and divalent cations and the exchangeable cations of the vermiculite ore, thus breaking and forming new bonds and generally weakening the binding forces holding the vermiculite platelets together.

The washing and subsequent soaking of this weakened structure with water causes osmotic swelling of the crystalline structure and allows it to be pulled apart or partially delaminated by vigorous agitation. The partially delaminated platelets may be further reduced in particle size by comminuting in a colloid mill or similar grindingshearing apparatus resulting in a water suspension of vermiculite platelets. At this point, the total sOlids content of the vermiculite suspension is adjusted to approximately 1 to 12 percent and contains l% of alkali metal chloride. This solution is fed to one of the compartments of the cell. The vermiculite is deposited from this solution onto the combustible materials by the mechanism described above.

The final product has a coating of vermiculite about 0.5 to 50 mils thick with a coating about 2 mils thick being preferred, since the addition of more vermiculite does not appreciably improve the properties of the product. The exceptional flameproofing characteristic of the product of our novel process is demonstrated by the wide variety of materials flameproofed. Good results are obtained when the fine suspension of vermiculite was applied to cotton cloth, nylon net, and cellulose, for example. After these products have been treated and dried, there is no tendency for the flame to propagate in any of the materials.

Inorganic materials have been used previously to inhibit the flame propagation of textiles and other flammable materials. However, the quantities required are usually suflicient to cause the material to become stiff. They are also characterized by an undesirable increase in weight and loss in resilience of the final product. Some of these compounds also cause a loss of tensile strength of the material being treated.

Fabrics or other flameproofed materials treated by our novel vermiculite composition do not lose tensile strength since the coating is applied as a very thin layer in the order of about 2 mils. The coating does not appreciably affect the hand or resilience of the fabrics.

The electrodeposition may be carried out using any suitable type of equipment. The deposition against a barrier is described above. The deposition can also be carried out by using a cylindrical cathode wrapped in the cloth or other material to be coated with the vermiculite.

The electrodeposition can be carried out in the presence of an electrolyte. However, since the platelets have a net electrical charge, the electrodeposition can be carried out without the use of an electrolyte. The electrolyte, when used, can be an organic nitrogen containing compound such as urea or a primary, secondary, tertiary amine having to 22 carbon atoms in the molecule, for example. This electrolyte is also useful in that is renders the deposit fast on the matrix being coated.

The electrodeposition of the coating on the fabric is normally completed using from about .5 to volts and l to 250 milliamperes for a period of about 2 to minutes. It is preferred to use a voltage of about 5 volts and a milliamperage of about 10-20 for periods of about 2 minutes.

Another important variable is the pH of the system. The system is normally maintained at a pH in the range of about 2 to 9, preferably about 6.0. An adherent coating on the fabric or other combustible material results in operation under these conditions.

Our invention is further illustrated by the following specific but non-limiting examples.

EXAMPLE I A series of runs are completed in which a cloth was coated with vermiculite. In this series, the electrolytic cell consisted of a platinum anode having an area of about 4 square inches and a cylindrical cathode with an area of about 18 square inches. The vermiculite to be used was exfoliated and treated with sodium chloride, then lithium chloride using the manner described previously. The electrolysis was carried out by diluting a lithium vermiculite slurry with 200 ml. of water to prepare a solution containing about 1 to 12 percent solids. Various electrolytes, such as diammonium phosphate and urea, were added. The cathode was wrapped with a piece of cloth and was rotated during the deposition. The deposition was carried out for varying periods of time using different power levels. The data collected in this series of runs are set out in the table below:

1 Cationic quaternary ammonium salts of the alkyl ammonium chloride typo. Made by Armour dz Co., Industrial Chemical Div. 2 A tallow amine made by Archer Daniel Midland Co.

All samples were air dried. The resulting coated papers were tough, flexible, flameproof, and water repellent.

EXAMPLE III The materials prepared by the processes described in Examples I and II were tested for flammability. To complete this test, strips measuring about 1 inch by 5 inches were cut and suspended with the longer dimension held vertically. A small gas flame about A to /2 inch long from a fine glass tip was then played for about 20 seconds on the long end of the strip. Observations were made with respect to:

(a) Ease of ignition,

(b) Ease of propagation or lack of propagation of the flame, and

(c) Tendency to afterglow.

The following table summarized the properties with respect to the compositions made from the fire retardants of Examples I and 11.

TABLE I pH of slurry Deposi- Electrolytic solution contained, vertion time, Current: At At Run No. miculitc minutes density start end 1 120 ml. of 1% K01 and 5 grams phos 40v.

photo in 300 ml. of water. 5 220 ma. 10. 4 9. 5 2 1111. of 1% KCl and 5 grams urea in 200 ml. of water. 5 ma. 7.0 7.0 3 1 gram ammornium chloride in 200 ml.

of water. 5 ma. 5.1 7.0 4 1 gram ammonium chloride in 230 ml.

01 water. 5 275 ma. .5. 1 7. 0 5 1 gram of ammonium nit-tote in 200 ml.

of water. 5 ma. 5. 0 7. 0

Norm-ma. milliamperos.

The product recovered from this series of runs had 60 TABLE In coatmg of vermiculite about 2 m1ls thick. The cloth dld not support combustion, in fact, a flame was extinguished Untreated E of 923i after a short contact with the vermiculite coated cloth. control I II Ease ofignition Easy DNC DNC. EXAMPLE H Propagation of flame Rapid None..." None.

(30 Afterglow tendency Appreciable do Do.

This example illustrated another method of preparing vermiculite coated paper. In this series of runs, a 0.85 weight percent slurry of vermiculite is charged to the cathode compartment and one of a variety of organic amine, acid salts and/or urea was charged to the anode compartment in concentrations varying from 0.1 to 10 weight percent. The two compartments are separated by glassine paper, thus, physically preventing the two solutions from mixing. The conditions for this operation are set out in the table below:

1 Did not catch.

It is obvious from review of these data that a flameresistant composition can be prepared by electrodeposition of vermiculite on glassine paper, cloth, and other normally combustible materials.

Obviously, many modifications and variations of the invention may be made without departing from the essence and scope thereof and only such limitations should be applied as are indicated in the appended claims.

What is claimed is:

1. A process for rendering combustible materials flame-resistant which comprises mounting said combustible material between two electrodes positioned in separate compartments in an electrolytic cell, impressing a potential across said electrodes and electrodepositing a layer of vermiculite from a slurry of exfoliated vermiculite in a solution of an alkali metal salt, containing up to 10% of an organic nitrogen electrolyte, onto said material, drying, and recovering the flame-resistant product.

2. The process according to claim 1 wherein the combustible material is cloth or paper in sheet form.

3. The process according to claim 1 wherein the electrodeposition is carried out using 0.5 to 50 volts and l to 250 milliamperes for a period of 1 to 30 minutes.

4. The process according to claim 1 wherein the alkali metal salt is lithium chloride in a concentration of less than 1% and the solution containing up to 10 percent of an organic nitrogen electrolyte.

5 atoms in the molecule.

7. The process according to claim 4 wherein the electrolyte is a secondary amine acid salt having 5 to 22 carbon atoms in the molecule.

8. The process according to claim 4 wherein the elec- 10 trolyte is a tertiary amine acid salt having 5 to 22 carbon atoms in the molecule.

References Cited UNITED STATES PATENTS 15 1,907,984 5/1933 Kraner 204 1s1 3,211,639 10/1965 McNeill et a1. 204181 1,884,110 10/1932 Morehouse 204-1s1 HOWARD S. WILLIAMS, Primary Examiner 

